炸蛋两粒 - Sounds the same and refers to 'Two Bombs!'. Soft boiled eggs, a common breakfast dish found in Kopitiams are always served in pairs, along with dark soy sauce and pepper. Egg is Ji Dan (鸡蛋) which sounds like Zha Dan (炸弹) – Bomb, in Mandarin. 
Thus the nickname, '炸蛋'.